What Causes Delayed Menstrual Periods And Negative Pregnancy Test?

I have not had a period for 6 months i dont not know why my husband and i had sex and i began to have cramps really bad after words for three days then i started spotting a brown discharge. and then finally my period comes and last for 4 days when i get off of it i have brown discharge and blood for one day then im tired all the type with heart burn and i have acne do you think i could be pregnant i took 2 pregnancy test and they both said negative but its only been ten days did i take them to early?